Abstract
1H-NMR is a very reproducible spectroscopic method and, therefore, a powerful tool for the metabolomic analysis of biological samples. However, due to the high complexity of natural samples, such as plant extracts, the evaluation of spectra is difficult because of signal overlap. The new NMR “Pure Shift” methods improve spectral resolution by suppressing homonuclear coupling and turning multiplets into singlets. The PSYCHE (Pure Shift yielded by Chirp excitation) and the Zangger–Sterk pulse sequence were tested. The parameters of the more suitable PSYCHE experiment were optimized, and the extracts of 21 Hypericum species were measured. Different evaluation criteria were used to compare the suitability of the PSYCHE experiment with conventional 1H-NMR. The relationship between the integral of a signal and the related bin value established by linear regression demonstrates an equal representation of the integrals in binned PSYCHE spectra compared to conventional 1H-NMR. Using multivariate data analysis based on both techniques reveals comparable results. The obtained data demonstrate that Pure Shift spectra can support the evaluation of conventional 1H-NMR experiments.
Highlights
Metabolomics is understood as a quantitative and comprehensive analysis of metabolites in a complex biological specimen to describe the chemical phenotype [1]
The PSYCHE experiment was optimized for the Hypericum plant extracts, representing complex mixtures of various compound classes
The extraction of quantitative information was possible from the binned PSYCHE spectra, and was not significantly different to the results from the binned conventional 1 H-Nuclear magnetic resonance (NMR)
Summary
Metabolomics is understood as a quantitative and comprehensive analysis of metabolites in a complex biological specimen to describe the chemical phenotype [1]. NMR is convincing due to its simple sample preparation process, high reproducibility, and non-destructive character [2,3] It was the method of choice for the structure elucidation of pure compounds; NMR is increasingly used nowadays for the analysis of complex mixtures [4]. 1 H-NMR spectrum is limited to a small spectral range, which leads to overlapping signals It is further strengthened by proton–proton scalar couplings, which cause multiplet structures. Besides the additional structural information, advantages in the untargeted metabolomics data processing Those studies handled samples with quantitative differences in metabolites, but just to a certain extent, they differed in their chemical composition. The best suitable Pure Shift method was determined, and the parameters were optimized to analyze complex extracts of different Hypericum species, which are known to vary in their major secondary metabolites [7]. The performance of the PSYCHE experiment within multivariate data analysis was addressed in terms of quantifiability, metabolite identification, and applicability
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